The present invention relates to a pipe heater manufacturing method for the manufacture of a pipe heater equipped with an electric resistor on the outer side of a stainless steel pipe and so formed that the fluid which is to be heated flows inside the pipe and also to a pipe heater produced by this manufacture method.
A rubber heater manufactured by a manufacturing method comprising the steps for coating the outer surface of a tubular member composed of a fluororesin tube with a silicone crude rubber sheet, winding a heat generating wire on top of the coating, coating a second silicon crude rubber sheet on top of it, winding an insulating material by tightly applying on top of the coating, heating at a temperature of 140–160° C. and curing the silicone crude rubber sheet in a semimolten state thereof, and producing an elastomer having the heat-generating wire embedded therein is known and described in, for example Laid-open Japanese Patent Application No. 2002-313542 (JP '542), and in particular FIG. 1 and the related explanation of the reference specification, where the reference teaches a pipe heater so formed that a fluid which is to be heated flows inside a pipe composed of any materials selected from a group of materials including stainless steel.
A pipe heater is also known which is manufactured by a manufacturing method comprising the steps for coating the outer surface of a pipe material with an insulating glass by any appropriate method, for example, a screen printing method, then baking to form an insulating glass layer, printing on top thereof a paste such as a silver-palladium paste by any appropriate method, for example, a screen printing method, then baking to form a resistor layer, and similarly forming a protective glass layer, such as described in Laid-open Japanese Patent Application No. 2002–83672 (JP '672), and in particular FIGS. 1, 2, 6 and the related explanation of the reference specification, where the reference teaches a pipe heater that is so formed that a fluid which is to be heated flows inside or outside a pipe composed of any material selected from a group of materials including stainless steel.
Those of the pipe heaters that are used, for example, for the below-described hydrogen supply apparatus and oxygen supply apparatus for a fuel cell evaluation device or for apparatuses for the fabrication of semiconductors or chemical machines and apparatuses are required to provide a high-level heating response and a high degree of cleanliness to prevent the penetration of foreign matter into the fluid which is to be heated.
With the rubber heater of JP' 542, the tubular member where the fluid flows is not heated to a high temperature in the manufacturing process. Therefore, if a stainless steel is used for the tubular member, it is maintained in a sufficiently clean state, without oxidation on the inner surface thereof. However, in rubber heaters, the elastomer composed of a silicone crude rubber sheet having a heat generating wire embedded therein has a low thermal conductivity and a large thickness. As a result, it has a high resistance to heat transfer and a large heat retention quantity and a long time is required to heat the rubber heater itself. The resultant problem is that a high-level heating response cannot be obtained.
In the pipe heater of JP '672, the insulating glass layer is formed by screen printing, the thickness thereof is sufficiently small and a high-level heating response can be obtained due to good thermal conductivity of glass. However, because the insulating glass layer is baked at a high temperature, even when a stainless steel is used for the tubular section, oxides are formed on the inner surface thereof due to high-temperature corrosion and there is a risk of those oxides penetrating into the fluid flowing inside the pipe. The resultant problem is that high-degree cleanliness of the inner surface of the pipe cannot be obtained.